Process for production of esters of unsaturated carboxylic acids

ABSTRACT

ESTERS OF UNSATURATED CARBOYXLIC ACID ARE OBTAINED FROM THE CORRESPONDING UNSATURATED ALDEHYDES IN A SINGLE STEP BY REACTING SAID ALDEHYDES WITH ALCOHOLS AND MOLECULAR OXYGEN IN THE PRESENCE OF AT LEAST A CATALYTIC AMOUNT OF PALLADIUM.

United States Patent O PROCESS FOR PRODUCTION OF ESTERS F UNSATURATED CARBOXYLMJ ACRES Seishiro Nakamura and Teruo Yasui, Kurashiki, Japan, assignors to Kuraray Co., Ltd., Kurashilri, Japan No Drawing. Filed June 1S, 1970, Ser. No. 47,619

Claims priority, application Japan, June 20, 1969,

Int. Cl. C07c 69/54 US. Cl. 260-486 R 13 Claims ABSTRACT OF THE DISCLOSURE Esters of unsaturated carboxylic acids are obtained from the corresponding unsaturated aldehydes in a single step by reacting said aldehydes with alcohols and molecular oxygen in the presence of at least a catalytic amount of palladium.

This invention relates to a process for the production of esters of unsaturated carboxylic acids, and more particularly, to a process for the production of esters of unsaturated carboxylic acids from unsaturated aldehydes, alcohols and molecular oxygen with the use of a palladium-containing catalyst.

Esters of unsaturated carboxylic acids, in particular esters of acrylic and methacrylic acids, are industrially important materials, and demands for said esters have been rapidly increasing in the fields of nitrile fibers and paints. These esters are useful also in the fields of leatherprocessing, paper-processing, adhesives and a starting material for organic glasses.

Esters of acrylic acid have heretofore been produced by, for example, the improved Reppe method utilizing acetylene as a starting material, the method comprising the alcoholysis of acrylonitrile, or the method utilizing ethylene cyanohydrin. Esters of methacrylic acid have generally been produced from acetone, via acetone cyanohydrin. However, none of these methods is sufficiently economical for commercial production of such esters in large quantities.

On the other hand, there has recently been developed a method for producing acrylic acid from propylene which comprises oxidizing propylene in gas phase to acrolein and then oxidizing said acrolein to acrylic acid, or oxidiz' ing propylene in a single step to acrylic acid. However, the yield of acrylic acid from said method is at most 50%. For this reason, it is not considered advantageous to produce esters of acrylic acid by the esterification of said acrylic acid. For the same reason, the production of esters of methacrylic acid from isobutylene, via methacrylic acid, is also not advantageous. However, the yield of acrolein in the gas phase oxidation of propylene and the yield of methacrolein in the gas phase oxidation of isobutylene are relatively high. For instance, the yield of acrolein can be expected to be more than 70%. Therefore, if said acrolein and methacrolein can be directly converted to esters of the corresponding unsaturated carboxylic acids, i.e., esters of acrylic acid and esters of methacrylic acid respectively, the production of said esters of unsaturated carboxylic acids will become much more advantageous as compared with conventional methods.

One object of the present invention is to provide a process according to which esters of unsaturated carboxylic acids can be directly produced in a single step from the corresponding unsaturated aldehydes. Other objects will be apparent from the ensuing description of this invention.

These objects can be attained by the process according to the present invention which comprises reacting an unsaturated aldehyde, an alcohol and molecular oxygen in the presence of at least a catalytic amount of palladium metal. Specifically, the inventors have now found that esters of unsaturated carboxylic acids can be obtained in good yields by reacting an unsaturated aldehyde, an alcohol and molecular oxygen in the presence of palladium metal catalyst.

It has now also been found that catalytic activity in said reaction can be increased by carrying out the reaction in the copresence of an alkali metal alkoxide.

According to the process of the present invention, esters of unsaturated carboxylic acids can be produced in a simplified and economical manner, and, for example, acrylic acid esters can be obtained very advantageously from acrolein because acrolein may be produced from propylene in higher yield than can acrylic acid. Similarly, methacrylic acid esters can be obtained very advantageously from methacrolein since methacrolein can be produced from isobutylene in higher yield than can methacrylic acid.

The reaction in accordance with the present invention can be carried out in either the gas phase or the liquid phase. Generally, the gas phase reaction is preferred. But, in the case where an unsaturated higher aldehyde and/ or higher alcohol is used as the starting unsaturated aldehyde and/or alcohol, the liquid phase reaction is often more desirable in view of the boiling point thereof.

The catalyst to be used in the process of the present invention should contain palladium metal. The catalyst may be unsupported, or supported on a suitable carrier such as alumina, silica, silica-alumina, pumice, activated carbon or the like. Alumina and silica are particularly preferable carrier materials. The amount of palladium metal to be supported on the carrier is usually in the range of about 0.1 to 5% by weight, preferably in the range of from 0.5 to 2% by weight, based on the weight of the carrier.

The addition of an alkali metal alkoxide such as potassium alkoxide or sodium alkoxide to the catalyst, and/or the reaction system, increases catalytic activity. The alkali metal alkoxide may be supported on the carrier and/ or be contained in the reactant or reactants. The amount of alkali metal alkoxide to be used is preferably in the range of about 1 to 10% by weight, based on the weight of the carrier, in the case where a supported palladium catalyst is used. The alkali metal alkoxides suitable for increasing catalytic activity include potassium alkoxide, sodium alkoxide and lithium alkoxide. Said alkoxides are preferably those of alcohols corresponding to alcohols used as the starting material in the reaction.

The alcohols and unsaturated aldehydes to be used as the starting materials in the reaction may be of any type. Examples of the preferable aldehydes include acrolein, methacrolein, crotonic aldehyde, and the like. Crotonic aldehyde may be used for the production of esters of crotonic acid. When the reaction is carried out in the gas phase, it is preferred to use an unsaturated aldehyde having a relatively low boiling point and alcohol having a relatively low boiling point. In whichever phase the reaction is conducted, all types of acrolein and methacholein are particularly preferably as the starting unsaturated aldehyde, and aliphatic alcohols having 1 to 5 carbon atoms such as methanol, ethanol, isopropanol and the like are particularly preferably as the starting alcohol.

The molar ratio of unsaturated aldehyde to alcohol may be within the range of about 120.1 to 1:10, and more preferably in the range of from 0.5 :1 to 3:1. An excessive supply of alcohol increases the by-production of saturated ester.

The amount of molecular oxygen to be used in the reaction may be varied over a relatively wide range. However, an excessive supply of oxygen in the gas phase reaction induces the combustion of aldehyde, alcohol and/or ester thereby increasing the formation of carbon dioxide. The preferred amount of oxygen to be supplied in the gas phase reaction is usually in the range of about 1 to 30% by volume, particularly in the range of from 3 to 10% by volume, based on the total volume of the starting gaseous mixture to be passed over the catalyst. The molecular oxygen may be supplied in the form of air in either liquid phase reaction or gas phase reaction, particularly in the liquid phase reaction. It is, however, preferred to use oxygen of relatively high purity in both gas phase reaction and liquid phase reaction. The alcohol and unsaturated aldehyde may be supplied after diluting the same with a diluting gas such as nitrogen, carbon dioxide or the like, if desired. Furthermore, the presence of water in the starting materials, for example in the starting gaseous mixture, to be supplied in the reaction does not affect the reaction.

The reaction may be carried out at a temperature of above 50 C., preferably at a temperature of from 80 C. to 200 C. The most preferable reaction temperatures are in the range of from 100 C. to 180 C. The use of higher temperatures results in increased formation of carbon dioxide. The reaction may be carried out under atmospheric pressure, or at reduced or elevated pressures. It is desirable to carry out the reaction under elevated pressures in order to increase the yield of the ester of unsaturated carboxylic acid. However, preferred pressures are less than 20 atmospheres, taking into consideration the reaction temperatures. In the gas phase reaction, a space velocity of the reaction mixture is preferably in the range of from 500 to 3000 volume/volume of catalyst-hour (i.e. 500 to 3000 hrr in other words 500 to 3000 vol./ vol. of catalyst per hour). In the liquid phase reaction, on the other hand, a suitable amount of catalyst (the amount of catalyst meaning total amount of palladium, carrier and alkali metal alkoxide, if the supported palladium catalyst, and an alkali metal alkoxide are used in the reaction) to be present in the reaction system is usually less than 50% by weight, preferably in the range of from 5 to 25% by weight, based on the weight of the reaction liquid.

The following examples are presented to further illustrate this invention.

EXAMPLE 1 Ten grams g.) of catalyst consisting of 1.0% by weight of palladium and 3% by weight of sodium methoxide supported on alumina having a surface area of 30 m. g. was put into a hard glass reaction tube of 10 millimeters inside diameter, and a gaseous mixture consisting of methanol, acrolein, oxygen and nitrogen at a volume ratio of methanol:acrolein:oxygenznitrogen of was introduced into the reaction tube at a flow rate of 3 liters per hour at 135 C. under a pressure of 1 atmosphere.

The reaction products were analyzed by gas chromatography, and it was confirmed that methyl acrylate had been formed at a rate of 10 g. per liter of catalyst per hour (=10 g./liter of catalyst-hour), methyl formate at a rate of 3 g./liter of catalyst-hour, and formaldehyde at a rate of 1 g./ liter of catalyst-hour. The efiluent gas contained 0.8% of carbon dioxide in addition to the products mentioned above.

EXAMPLE 2 Using the same catalyst and apparatus as were used in Example 1, the reaction was conducted at 120 C. and under a pressure of 1 atm. by introducing a gaseous mixture consisting of ethanol, acrolein, oxygen and carbon dioxide at a volume ratio of 20:35:7z38 into the reaction tube at a flow rate of 2 liters per hour.

As a result, ethyl acrylate was formed at a rate of 6 g./liter of catalyst-hour, acetaldehyde at a rate of 2 g./liter of catalyst-hour and ethyl acetate at a rate of 3 g./liter of catalyst-hour. The efiluent gas contained also 0.6% of carbon dioxide formed.

4 EXAMPLE 3 Ten grams (10 g.) of catalyst consisting of 2% by weight of palladium supported on silica (the catalyst being in the shape of tablets of 3 millimeters in both diameter and height, and having been prepared from commercial powdered silica) was put into the same reaction tube as was used in Example 1, and a gaseous mixture consisting of methanol, acrolein, oxygen and nitrogen in a volume ratio of 30:30: 10:30 was introduced into the reaction tube at a flow rate of 5 liters per hour at 150 C. under a pressure of 1 atmosphere.

As a result, methyl acrylate was formed at a rate of 13 g./liter of catalyst-hour, and methyl formate at a rate of 5 g./liter of catalyst-hour. Formaldehyde was formed in a trace amount. The efiluent gas contained 1.8% of carbon dioxide.

EXAMPLE 4 Alumina beads of 3 millimeters in diameter (Neobead alumina beads, a product of Mizusawa Kagaku Kogyo Kabushiki Kaisha, Japan) was calcined at 1000 C. On said alumina were supported 1.0% by weight of palladium and 2% by weight of potassium methoxide. Ten grams (10 g.) of the catalyst thus prepared was put into the same reaction tube as was used in Example 1, and a gaseous mixture consisting of methacrolein, methanol, oxygen and nitrogen in a volume ratio of 40:10:10140 was introduced into the reaction tube at a flow rate of 3 liters per hour at 135 C. and under a pressure of 1 atm.

As a result, methyl methacrylate was formed at a rate of 11 g./liter of catalyst-hour, methyl formate at a rate of 3 g./ liter of catalyst-hour, and formaldehyde at a rate of 2 g./liter of catalyst-hour. The eflluent gas contained 0.9% of carbon dioxide.

EXAMPLE 5 Ten grams (10 g.) of catalyst consisting of 2% by weight of palladium supported on alumina having a particle size of 200 to 300 mesh was charged into an autoclave (the capacity of which was 100 cc.) with an electromagnetic stirrer together with a liquid mixture consisting of 15 cc. of methanol and 35 cc. of acrolein, and then air was introduced into said autoclave up to an elevated pressure of 10 atmospheres and the reaction was performed while maintaining the temperature of C.

The reaction was continued for 3 hours and thereafter the reaction products were analyzed. It was found that 0.25 g. of methyl acrylate and 0.08 g. of methyl formate had been formed.

What is claimed is:

1. A process for the production of esters of unsaturated carboxylic acids which comprises reacting an unsaturated aldehyde, an alcohol and molecular oxygen in the presence of at least a catalytic amount of palladium and an alkali metal alkoxide to thereby produce the corresponding unsaturated ester.

2. A process according to claim 1, wherein the palladium and alkali metal alkoxide are supported on a carrier.

3. A process according to claim 1, wherein the unsaturated aldehyde is acrolein and the esters are esters of acrylic acid.

4. A process according to claim 1, wherein the unsaturated aldehyde is methacrolein and the esters are esters of methacrylic acid.

5. A process according to claim 1, wherein the alcohol is a lower aliphatic monohydric alcohol.

6. A process according to claim 5, wherein the lower aliphatic monohydric alcohol is methanol.

7. A process according to claim 5, wherein the lower aliphatic monohydric alcohol is ethanol.

8. A process according to claim 1, wherein the molar ratio of unsaturated aldehyde to alcohol is in the range of about 1:0.1 to 1:10.

9. A process according to claim 8, wherein the molar ratio of unsaturated aldehyde to alcohol is in the range of 0.5:1 to 3:1.

10. A process according to claim 1, wherein the reaction is carried out at a temperature of from 80 C. to 200 C.

11. A process according to claim 1, wherein the reaction is carried out under a pressure of from 1 to 20 atmospheres.

12. A process according to claim 2, wherein the amount of palladium supported on the carrier is in the range of 0.1 to 5% by weight, based on the weight of the carrier.

13. A process according to claim 2, wherein the amount of alkali metal alkoxide supported on the carrier is in the 6 References Cited UNITED STATES PATENTS 3,639,449 2/1972 Kunugi et a1 260486 R 3,230,248 1/ 1966 Yanagita et a1 260-486 R 3,253,025 5/1966 Brill et a1 260-486 R FOREIGN PATENTS 1,068,450 5/1965 Great Britain 260486 R 10 LORRAINE A. WEINBERGER, Primary Examiner P. J. KILLOS, Assistant Examiner U.S. Cl. X.R.

range of about 1 to 10 by weight, based on the weight of 15 603 HP the carrier. 

